Four Cisco Systems executives who led "spin-in" ventures that became important parts of the company have resigned.

The longtime leaders decided to leave the company on June 17 because of "a disconnect regarding roles, responsibilities and charter" after a new Cisco business unit was announced, according to an internal memo posted Monday by CEO Chuck Robbins and seen by IDG News Service. The move was first reported by the Wall Street Journal.

Engineers Mario Mazzola, Prem Jain, and Luca Cafiero, and marketer Soni Jiandani, nicknamed "MPLS" after their first initials, started several companies with Cisco’s backing that later were absorbed back into the networking giant. The companies included Andiamo Networks in storage, Nuova Systems in data-center switching and Insieme Networks in SDN (software-defined networking).

The four resigned after Cisco announced the formation of the Networking & Security Business Group, which will handle engineering for routing, switching and security products, the memo said. David Goeckeler, a 16-year Cisco veteran, leads the group. Starting June 17, the Insieme business unit will also become part of it.

Cisco brought the four on board when it bought LAN switching vendor Crescendo Communications in 1993, the company’s first major acquisition. More than once, Cisco invested in startups spearheaded by MPLS and then acquired those companies.

That was under former CEO John Chambers, who stepped down last year after 20 years leading the company. He is still Cisco’s chairman, and MPLS continued to report to Chambers after Robbins succeeded him, sources told Network World last August.

In a statement on Monday, Robbins praised the outgoing executives.

"I want to recognize Mario, Prem, Luca, and Soni for the countless contributions they have made to Cisco. I have personally learned so much from them, and they will always be an important part of Cisco’s engineering story," he said. "Their legacy will live on through our ongoing innovation and the talented engineering leaders they have mentored."

Robbins has made major changes in Cisco’s leadership as he puts his own mark on the 32-year-old company. Sanjiv Ahuja, leader of the service-provider business, resigned in March.